In a nuclear power plant, the nuclear reactor and most of the components associated with the reactor are typically enclosed within a containment building. The containment building may be constructed of reinforced concrete, having walls several feet thick. The containment building serves to trap radioactive debris and protect the outside environment in the event of an accident.
Unfortunately, if the accident results in the generation of sufficiently high pressures, the containment building may rupture. Radioactive debris will then be scattered over a wide area and any radioactive components remaining in the ruptured containment building may be exposed to the outside environment.